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[mediawiki.git] / includes / libs / StringUtils.php

<?php
/**
 * Methods to play with strings.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 * http://www.gnu.org/copyleft/gpl.html
 *
 * @file
 */

/**
 * A collection of static methods to play with strings.
 */
class StringUtils {
        /**
         * Test whether a string is valid UTF-8.
         *
         * The function check for invalid byte sequences, overlong encoding but
         * not for different normalisations.
         *
         * This relies internally on the mbstring function mb_check_encoding()
         * hardcoded to check against UTF-8. Whenever the function is not available
         * we fallback to a pure PHP implementation. Setting $disableMbstring to
         * true will skip the use of mb_check_encoding, this is mostly intended for
         * unit testing our internal implementation.
         *
         * @note In MediaWiki 1.21, this function did not provide proper UTF-8 validation.
         * In particular, the pure PHP code path did not in fact check for overlong forms.
         * Beware of this when backporting code to that version of MediaWiki.
         *
         * @since 1.21
         * @param string $value String to check
         * @param bool $disableMbstring Whether to use the pure PHP
         *  implementation instead of trying mb_check_encoding. Intended for unit
         *  testing. Default: false
         * @return bool Whether the given $value is a valid UTF-8 encoded string
         */
        static function isUtf8( $value, $disableMbstring = false ) {
                $value = (string)$value;

                // If the mbstring extension is loaded, use it. However, before PHP 5.4, values above
                // U+10FFFF are incorrectly allowed, so we have to check for them separately.
                if ( !$disableMbstring && function_exists( 'mb_check_encoding' ) ) {
                        static $newPHP;
                        if ( $newPHP === null ) {
                                $newPHP = !mb_check_encoding( "\xf4\x90\x80\x80", 'UTF-8' );
                        }

                        return mb_check_encoding( $value, 'UTF-8' ) &&
                                ( $newPHP || preg_match( "/\xf4[\x90-\xbf]|[\xf5-\xff]/S", $value ) === 0 );
                }

                if ( preg_match( "/[\x80-\xff]/S", $value ) === 0 ) {
                        // String contains only ASCII characters, has to be valid
                        return true;
                }

                // PCRE implements repetition using recursion; to avoid a stack overflow (and segfault)
                // for large input, we check for invalid sequences (<= 5 bytes) rather than valid
                // sequences, which can be as long as the input string is. Multiple short regexes are
                // used rather than a single long regex for performance.
                static $regexes;
                if ( $regexes === null ) {
                        $cont = "[\x80-\xbf]";
                        $after = "(?!$cont)"; // "(?:[^\x80-\xbf]|$)" would work here
                        $regexes = array(
                                // Continuation byte at the start
                                "/^$cont/",

                                // ASCII byte followed by a continuation byte
                                "/[\\x00-\x7f]$cont/S",

                                // Illegal byte
                                "/[\xc0\xc1\xf5-\xff]/S",

                                // Invalid 2-byte sequence, or valid one then an extra continuation byte
                                "/[\xc2-\xdf](?!$cont$after)/S",

                                // Invalid 3-byte sequence, or valid one then an extra continuation byte
                                "/\xe0(?![\xa0-\xbf]$cont$after)/",
                                "/[\xe1-\xec\xee\xef](?!$cont{2}$after)/S",
                                "/\xed(?![\x80-\x9f]$cont$after)/",

                                // Invalid 4-byte sequence, or valid one then an extra continuation byte
                                "/\xf0(?![\x90-\xbf]$cont{2}$after)/",
                                "/[\xf1-\xf3](?!$cont{3}$after)/S",
                                "/\xf4(?![\x80-\x8f]$cont{2}$after)/",
                        );
                }

                foreach ( $regexes as $regex ) {
                        if ( preg_match( $regex, $value ) !== 0 ) {
                                return false;
                        }
                }

                return true;
        }

        /**
         * Perform an operation equivalent to `preg_replace()`
         *
         * Matches this code:
         *
         *     preg_replace( "!$startDelim(.*?)$endDelim!", $replace, $subject );
         *
         * ..except that it's worst-case O(N) instead of O(N^2). Compared to delimiterReplace(), this
         * implementation is fast but memory-hungry and inflexible. The memory requirements are such
         * that I don't recommend using it on anything but guaranteed small chunks of text.
         *
         * @param string $startDelim
         * @param string $endDelim
         * @param string $replace
         * @param string $subject
         * @return string
         */
        static function hungryDelimiterReplace( $startDelim, $endDelim, $replace, $subject ) {
                $segments = explode( $startDelim, $subject );
                $output = array_shift( $segments );
                foreach ( $segments as $s ) {
                        $endDelimPos = strpos( $s, $endDelim );
                        if ( $endDelimPos === false ) {
                                $output .= $startDelim . $s;
                        } else {
                                $output .= $replace . substr( $s, $endDelimPos + strlen( $endDelim ) );
                        }
                }

                return $output;
        }

        /**
         * Perform an operation equivalent to `preg_replace_callback()`
         *
         * Matches this code:
         *
         *     preg_replace_callback( "!$startDelim(.*)$endDelim!s$flags", $callback, $subject );
         *
         * If the start delimiter ends with an initial substring of the end delimiter,
         * e.g. in the case of C-style comments, the behavior differs from the model
         * regex. In this implementation, the end must share no characters with the
         * start, so e.g. `/*\/` is not considered to be both the start and end of a
         * comment. `/*\/xy/*\/` is considered to be a single comment with contents `/xy/`.
         *
         * The implementation of delimiterReplaceCallback() is slower than hungryDelimiterReplace()
         * but uses far less memory. The delimiters are literal strings, not regular expressions.
         *
         * @param string $startDelim Start delimiter
         * @param string $endDelim End delimiter
         * @param callable $callback Function to call on each match
         * @param string $subject
         * @param string $flags Regular expression flags
         * @throws InvalidArgumentException
         * @return string
         */
        static function delimiterReplaceCallback( $startDelim, $endDelim, $callback,
                $subject, $flags = ''
        ) {
                $inputPos = 0;
                $outputPos = 0;
                $output = '';
                $foundStart = false;
                $encStart = preg_quote( $startDelim, '!' );
                $encEnd = preg_quote( $endDelim, '!' );
                $strcmp = strpos( $flags, 'i' ) === false ? 'strcmp' : 'strcasecmp';
                $endLength = strlen( $endDelim );
                $m = array();

                while ( $inputPos < strlen( $subject ) &&
                        preg_match( "!($encStart)|($encEnd)!S$flags", $subject, $m, PREG_OFFSET_CAPTURE, $inputPos )
                ) {
                        $tokenOffset = $m[0][1];
                        if ( $m[1][0] != '' ) {
                                if ( $foundStart &&
                                        $strcmp( $endDelim, substr( $subject, $tokenOffset, $endLength ) ) == 0
                                ) {
                                        # An end match is present at the same location
                                        $tokenType = 'end';
                                        $tokenLength = $endLength;
                                } else {
                                        $tokenType = 'start';
                                        $tokenLength = strlen( $m[0][0] );
                                }
                        } elseif ( $m[2][0] != '' ) {
                                $tokenType = 'end';
                                $tokenLength = strlen( $m[0][0] );
                        } else {
                                throw new InvalidArgumentException( 'Invalid delimiter given to ' . __METHOD__ );
                        }

                        if ( $tokenType == 'start' ) {
                                # Only move the start position if we haven't already found a start
                                # This means that START START END matches outer pair
                                if ( !$foundStart ) {
                                        # Found start
                                        $inputPos = $tokenOffset + $tokenLength;
                                        # Write out the non-matching section
                                        $output .= substr( $subject, $outputPos, $tokenOffset - $outputPos );
                                        $outputPos = $tokenOffset;
                                        $contentPos = $inputPos;
                                        $foundStart = true;
                                } else {
                                        # Move the input position past the *first character* of START,
                                        # to protect against missing END when it overlaps with START
                                        $inputPos = $tokenOffset + 1;
                                }
                        } elseif ( $tokenType == 'end' ) {
                                if ( $foundStart ) {
                                        # Found match
                                        $output .= call_user_func( $callback, array(
                                                substr( $subject, $outputPos, $tokenOffset + $tokenLength - $outputPos ),
                                                substr( $subject, $contentPos, $tokenOffset - $contentPos )
                                        ) );
                                        $foundStart = false;
                                } else {
                                        # Non-matching end, write it out
                                        $output .= substr( $subject, $inputPos, $tokenOffset + $tokenLength - $outputPos );
                                }
                                $inputPos = $outputPos = $tokenOffset + $tokenLength;
                        } else {
                                throw new InvalidArgumentException( 'Invalid delimiter given to ' . __METHOD__ );
                        }
                }
                if ( $outputPos < strlen( $subject ) ) {
                        $output .= substr( $subject, $outputPos );
                }

                return $output;
        }

        /**
         * Perform an operation equivalent to `preg_replace()` with flags.
         *
         * Matches this code:
         *
         *     preg_replace( "!$startDelim(.*)$endDelim!$flags", $replace, $subject );
         *
         * @param string $startDelim Start delimiter regular expression
         * @param string $endDelim End delimiter regular expression
         * @param string $replace Replacement string. May contain $1, which will be
         *  replaced by the text between the delimiters
         * @param string $subject String to search
         * @param string $flags Regular expression flags
         * @return string The string with the matches replaced
         */
        static function delimiterReplace( $startDelim, $endDelim, $replace, $subject, $flags = '' ) {
                $replacer = new RegexlikeReplacer( $replace );

                return self::delimiterReplaceCallback( $startDelim, $endDelim,
                        $replacer->cb(), $subject, $flags );
        }

        /**
         * More or less "markup-safe" explode()
         * Ignores any instances of the separator inside `<...>`
         * @param string $separator
         * @param string $text
         * @return array
         */
        static function explodeMarkup( $separator, $text ) {
                $placeholder = "\x00";

                // Remove placeholder instances
                $text = str_replace( $placeholder, '', $text );

                // Replace instances of the separator inside HTML-like tags with the placeholder
                $replacer = new DoubleReplacer( $separator, $placeholder );
                $cleaned = StringUtils::delimiterReplaceCallback( '<', '>', $replacer->cb(), $text );

                // Explode, then put the replaced separators back in
                $items = explode( $separator, $cleaned );
                foreach ( $items as $i => $str ) {
                        $items[$i] = str_replace( $placeholder, $separator, $str );
                }

                return $items;
        }

        /**
         * Escape a string to make it suitable for inclusion in a preg_replace()
         * replacement parameter.
         *
         * @param string $string
         * @return string
         */
        static function escapeRegexReplacement( $string ) {
                $string = str_replace( '\\', '\\\\', $string );
                $string = str_replace( '$', '\\$', $string );
                return $string;
        }

        /**
         * Workalike for explode() with limited memory usage.
         *
         * @param string $separator
         * @param string $subject
         * @return ArrayIterator|ExplodeIterator
         */
        static function explode( $separator, $subject ) {
                if ( substr_count( $subject, $separator ) > 1000 ) {
                        return new ExplodeIterator( $separator, $subject );
                } else {
                        return new ArrayIterator( explode( $separator, $subject ) );
                }
        }
}